Why Traffic Protection in Transport Network?

A. Bellato CTO T&A Team - OND 10

Users Dependency in Telecoms

ESTIMATED BUSINESS LOSS DUE TO TELECOMSSERVICE FAILURE, AN FCA (US) REPORT:$107000 PER MINUTE IN A BROKERAGE INSTITUTION$47000 PER MINUTE IN A CREDIT CARD/SALES AUTHORISATION$2500 PER MINUTE IN A PAY PER VIEW$1800 PER MINUTE IN A HOME SHOPPING (TV)$1500 PER MINUTE IN A CATALOG SALES$1500 PER MINUTE IN AN AIRLINE RESERVATION BOOTH

A. Bellato CTO T&A Team - OND 11

Price Sensitivity in Public Telecom Operators SLAs

EXAMPLES OF NATIONAL OPERATORS SERVICE LEVEL AGREEMENTS

GUARANTEED MAXUAT

GUARANTEED MAXMTTR

FINANCIALPENALTY

PRICE PREMIUM

EU Premium: 1 2Hour/Year

4 8 Hours

10% of a month2 months

15 50%

EU Standard: 4 13Hour/ Year

4 8 Hours

1 month - 1yearrevenue fees

10 15%

A. Bellato CTO T&A Team - OND 12

Content>

Transport Network Concept

>

Need for traffic protection

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Methods for traffic protection: Protection &

Restoration

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Basics for traffic protection

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Protection Schemes in Transport Networks

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APPENDIX: Protection schemes in SDH/ Sonet/ OTN

A. Bellato CTO T&A Team - OND 13

Network Topologies

Ring Based

Eventualclosure

Mesh Based

Linear

Ring BasedLinearEventualclosure

Mediumdensityof populationPOPULATION IS CONSIDERED ASAMOUNT OF NETWORKELEMENTS TO BE CONNECTED

A. Bellato CTO T&A Team - OND 14

High densityof population

Low densityof population

PROTECTIONProtection is a method for the traffic recovery, considered ashigh priority traffic (Normal traffic) , usually associated toa fast process where the Network Elements (NE)autonomously decide when to act (selfhealing). The protection algorithm is implemented and handled byNEs The protection application makes use of preassignedcapacitybetween nodes (protection transport entity) The alternative path used for traffic recovery, has aeither apredefined routing or it is allocated throughpredefined links Protection transport entity can carry low priorityA.trafficBellato CTO T&A Team - OND(Extra15Traffic) when not in switching condition

Protection applicationHGIF

LA

Switch time 50 300 ms

E

Working circuit path: GFHIL

Failure on section: HI Predefined alternative path (protection path) on GEABL Protection transport entity can be used for the transport of low riority traffic(depending on the specific protection scheme)

A. Bellato CTO T&A Team - OND 16

RESTORATIONRestoration is a method for the traffic recovery, usuallyassociated to a slower process, where the switchingdecision is taken by a Network Management System(NMS) which can be either centralized or distributedthrough the network.

The restoration application makes use of any capacity

available between nodes, depending on failurescenario and on traffic matrix The restored path doesn't have a unique predefinedrouting.

Bidirectional Uniform routing

The traffic is routed on

The traffic shares the same

Switching Mode Possible Advantages

Advantages of unidirectional protection switching: simplicity of implementation: no protocol required but double bandwidth used best switch time performance, than bidirectional protection switching,due tothe lack of protocol message exchange greater chance of restoring traffic, than bidirectional protectionswitching, but diverse routing

Advantages of bidirectional protection switching:

greater efficiency of bandwidth usage, than unidirectional protectionswitching,due to the ability of supporting extra-traffic on protection pathwhen no switching is required chance to get easier maintenance operations due to uniform routing:traffic travels inboth directions either along the working path or the protectionpath, then, one path is activethe alternative path is standby (reduced number of sites possibly interested) equal delay for both directions of transmission, significant feature withtransoceanic links and via-satellite linksA. Bellato CTO T&A Team - OND 28

Operation Mode In revertive operation mode, the traffic signal always returns to theworking transport entity, when it has recovered from the defect or the externalrequest is cleared(revertive operation is handled either unidirectionallyor bidirectionally consistently to the switching mode of the protectionscheme)Revertive unidirRevertive bidirEnd 1 Working

Protection

End 2

End 1 Working

End 2

Protectionbidirectional revert switchtriggered by APS signaling

In nonrevertive operation mode, the traffic signal does not return to theworking transport entity, once the defect or the external request affectingworking resource hasbeen removed.

A. Bellato CTO T&A Team - OND 29

Operation Mode Application

The not revertive operation mode is applicable only where a workingtransport resource has a dedicated protection resource (e.g. protection schemewith unidirectional switching mode). Advantage: glitch on traffic, due to revert switch, avoided, then trafficperformanceincreased.

The revertive operation mode is applicable both in case of protection

resource dedicated to a working resource and in case of protection resourceshared amongdifferent working transport entities. The revertive mode isappropriate when: the protection resource capacity is required to restore other traffic signal,due to more urgent need (e.g., protection scheme with shared protection transportentity) the protection resource may be subject to frequent re-arrangement (e.g.where anetwork has limited capacity and protection routes are frequently rearranged to maximize network efficiency when changes occur in the network) the protection resource is of significantly lower performance than theworking resource (e.g. where the protection transport entity has a worse errorperformance or longer delay than the working transport entity) an operator needs to know which transport entities are carrying normaltraffic in order to simplify the management of the networkA. Bellato CTO T&A Team - OND 30

Switching Initiation Criteria

are, those conditions able to START (initiate), at a NetworkElement, a protection activity (i.e. a state machine evolution).Specifically:AUTOMATICALLYINITIATEDCOMMANDS

Fault conditions affecting the

traffic to be protected at thespecific layerIN DETAILS

EXTERNALLYINITIATEDCOMMANDS

A. Bellato CTO T&A Team - OND 33

Available commands allowing the

operator to control protectionalgorithm, by forcing, pre-emptingor testing the switching status

Automatically Initiated Commands

Signal FailAll the defect conditions producing the unavailability of thetraffic to be protected at the interested layerSignal DegradeError condition affecting traffic to be protected at the interestedlayer, over a specific threshold set by operator (not necessarilyproducing a unavailability)

A. Bellato CTO T&A Team - OND 34

Externally Initiated Commands

Configuration modification and maintenanceLockout of Protection makes the protection transport entity unavailable for (all)the Normal Traffic(s) to be protectedForced Switch (#n) forces Normal Traffic (#n) to be routed over the protectiontransport entityManual Switch (#n) routes Normal Traffic (#n) over the protection transport entityunless a fault condition (SF, SD) requires another signal to be routed over thistransport entityControl CommandsLockout of Working (#n) disables the access to the protection transport entity forthe (specific) Normal TrafficClear Lockout of Working (#n) clears the Lockout of Working (#n) command

A. Bellato CTO T&A Team - OND 35

Externally Initiated Commands

In bidirectional switching mode systems, testing of APS protocolExercise (#n) emulates a switch request (for Normal Traffic #n) without performingany actual switch action, unless the protection transport entity is being usedClearing previous external command (not addressable by other specificclear command)Clear clears all the switch commandsFreeze the protection process (commands under standardization)Freeze the current state of the Protection Algorithm Controller (mainly thought forchecking the APS protocol exchange for APS Controller)Clear Freeze clears the Freeze command and allows the Protection AlgorithmController to evolve on the base of current inputs stateA. Bellato CTO T&A Team - OND 36

Protection Switching Performance

Switch InitiationTime(or Detection Time)Time interval between theoccurrence of a networkimpairment and thedetection of a signal fail(SF) or signal degrade (SD)triggered by that networkimpairment

Hold-Off TimeTime interval after thedetection of a SF or SDand its confirmation as acondition requiring theprotection switchingprocedure

Switch CompletionTimeThe interval from thedecision to switch(including time needed toachieve this decision) to thecompletion of the bridgeand switch operation at aswitching node initiating thebridge request

Time

Network Impairment

SF SD trigger

A. Bellato CTO T&A Team - OND 37

Start of protectionSwitching operations(SF-SD confirmation)

Protected trafficrestored

Content>

Transport Network Concept

>

Need for traffic protection

>

Methods for traffic protection: Protection & Restoration

>

Basics for traffic protection

DefinitionsSwitching CriteriaProtection Architectures

>

Protection Schemes in Transport Networks

>

APPENDIX: Protection schemes in SDH/ Sonet/ OTN

A. Bellato CTO T&A Team - OND 38

Protection Architecture Linear

Linear protection architecture is applicable to both linear and ringnetwork topology: only End nodes performs a protection activity,due to the resident Protection Algorithm Controller

N.T.

N.T.

NE 1

P.A.C.

Intermediate node performing

traffic cross-connection and alarm(defects / errors) propagation

P.A.C.

NE 3(Pr)

NE 1(Wk)

NE 4

NE 3(Pr)

NE 2

(Wk)

NE 4NE 2

P.A.C.

P.A.C.

N.T.

N.T.

Linear network topology

A. Bellato CTO T&A Team - OND 39

Ring network topology

Protection Architecture Linear

Linear protection architecture is also applicable to meshed network topology,whenever two separated paths (working and protection) can be identified throughthe network: again, only End nodes performs a protection activity, due to theresident Protection Algorithm ControllerN.T.(Wk)

2F (fiber) ring network topology

4F (fiber) ring network topo

Protection Architecture SPRing

N.T.(Wk)(Pr)

N.T.

Meshed network topology

A. Bellato CTO T&A Team - OND 42

SPRing protection architecture is also

applicable to meshed network topology,whenever a closed connection of NEs(i.e. a ring) is identified through thenetwork: again, every node of the ring,performs a protection activity, due to theresident Protection Algorithm Controller

Bridge & Switch

Linear APS channel content

Protocol Parameters Request Type i.e. the request (failure / degrade / command) or state (No Request /Do Not Revert / WTR) to be signalled / acknowledged by each end ofthe protection group Requesting Channel Identifier i.e. the identifier of working / protection resourcefor which the request type is issued

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In Idle state (no protection required through the

ring), N.T. is on working resources, E.T. may beconfigured on protection resources. Protocolsignaling carries No request code from each nodeto the adjacent one

2F classic SPRing Ring Switch

N.T. recovered E.T. squelched

Bridge to x+N/2 Protection

resources

SHORT

PATH

Switch to x+N/2 Protection

resources

NE 1Working resourcex

Bridge

NE 4

E.T.squelched

NE 2

Switch

P.T.

Protection resourcesN/2+1 NPass-throughPATH

NE 3

LONG

N.T. recovered E.T. squelched

Working resourcesProtection resources

A. Bellato CTO T&A Team - OND 61

Squelching(AIS injection)

2F classic SPRing Ring Switch

Ring Switch recovers Normal Trafficthrough protection resources on the LONGpath, when bothworking and protection resources of a span are failure/degrade affectedor when a ring command (Force / Manual)is applied.- In 2F topology this scenario occurs anytime a failure/degrade affects at least one out oftwo transmission means of a span, or when a ring command is applied on that span. During ring switch all the Extra Traffics configured through the ring are squelched(regardless of the actual use of that channel for Normal Traffic protection). The following node macro-states are entered during protection activity:Switching Macro-state entered by end nodes of the span interested with switchingcriteria, both initiating a ring switch by sending (tail end) to the adjacent switching node,both on the LONG and on the SHORT path of the ring a ring bridge request, oracknowledging (head end), both on LONG / SHORT path a ring bridge request destined toitself.In classic application, only switchingnodes performs ring Bridge&Switch, on the base of APS signaling exchanged through theLONG path(see yellow nodes in previous example)Full Pass-through Macro-state entered by each node of the ring (not switching), bypassing bridge request not destined to itself; performing also the bidirectional by-pass(EW, W E) of protection resources (Low Priority channels). Pass-through nodes arealso called intermediate nodes.(see grey nodes in previous example)

In classic application (2F/4F) the

When applied to huge rings including

transoceanic links or via satellitelinks, and depending on the type ofservice transported, this delay can leadto a final performance degradation ofE.T.the servicesquelched

Bridge

Bridge

P.T.

NE 4

NE 2

Switch

P.T.

PATH

NE 3

LONG

N.T. recovered E.T. squelched

A. Bellato CTO T&A Team - OND 63

Squelching(AIS injection)

Working resourcesProtection resources

4F transoceanic SPRing Ring Switch

N.T. recovered E.T. squelched

SHORT

PATH

In transoceanic application (4F) the

protection path in ring switch condition,corresponds to the LONG path of thescheme only when the protected NormalTraffic is configured between adjacentnodes.

Switch

NE 1

With different traffic distribution (where

node pass-through occurs) the protectionpath is limited to the portion of the ring,not fault affected, between nodesE.T.terminating the protected Normal Traffic.squelched

Bridge

Pass-through

NE 4

NE 2Switch

NE 3

Temporary squelching, if associated LP channels

are not required for ring switch connectivityPATH

Bridge

LONG

N.T. recovered E.T. squelched

A. Bellato CTO T&A Team - OND 64

4F SPRing Ring Switch - I

Ring Switch, in 4F topology occurs anytime a failure/degrade affects at least two out offour transmission means of a span, in such a way that both one working and oneprotection resources results fault affected or when a ring command is applied on that span. Asfor 2F ring, Normal Traffic isrecovered through protection resources on the LONG path. In classic (also called terrestrial) application, same behaviour already described about2F ring,sameE.T. squelching policy and same node macro-states apply. In transoceanic application, current standard reference (SDH) states that during ringswitch all the Extra Traffics configured through the ring are squelched; after the ring switchis performed, thoseLow Priority channels not used for Normal Traffic protection are reconnected to Extra Traffic.This is a slow process possibly using communication channels between the nodes of thering, i.e. control plane, for E.T. re-configuration (protection protocol independent).Both distributed ring switch and Extra Traffic recovery is applicable, due to the knowledgeof the wholering connectivity at each node of the ring (see Traffic Map).The following node macro-states are entered during protection activity:

A. Bellato CTO T&A Team - OND 65

4F SPRing Ring Switch - II

Switching Macro-state entered by end node of the span interested with switchingcriteria, initiating aring switch by sending (tail end) to the adjacent switching node, bothon the LONG and on theSHORT path of the ring a ring bridge request, or acknowledging(head end), both on LONG/SHORT path a ring bridge request destined to itself.Switching nodes performs ringBridge&Switch only when adding/dropping (terminating) Normal Traffic to be protected on thebase of APS signaling exchanged through the LONG path (see yellow nodes in previousexample).Full Pass-through Macro-state entered by each node of the ring (not switching), bypassing bridge request not destined to itself. The same protocol specified in classicapplication is used.Pass-through nodes performs ring Bridge&Switch only whenadding/dropping (terminating) Normal Traffic to be protected on the base of APS signalingreceived by both switching nodes; otherwise, they realize the bidirectional by-pass (EW,W E) of protection resources (Low Priority channels). Pass-through nodes are also calledintermediate nodes (see grey nodes in previous example).

N.T. recovered E.T. kept

A. Bellato CTO T&A Team - OND 68

The protection path corresponds

always to the SHORT path of thescheme: i.e. Normal Traffic is recoveredthrough the same span alongprotection resource.

4F SPRing Span switch

Span Switch, in 4F topology (both classic and transoceanic applications) occursanytime a failure/degrade affects only the working transmission mean of a span in one orboth directions or a span command is applied. NormalTraffic is recovered through theassociated protectionresource of thatspan by using the same algorithm alreadydescribed for linear 1:N scheme. During span switch (both classic and transoceanic applications) all the Extra Trafficsconfigured in the span fault affected are squelched; while remaining E.T. allocated indifferent spans of the ring are kept.In transoceanic application, those L.P. channels notrequired for span switch connectivity, then the associated E.T., are restoredafter spanswitch is performed (same way already described for ringswitch). The following node macro-states are entered during protection activity:Switching Macro-state entered by end node of the span interested with switchingcriteria, initiating a span switch by sending (tail end) to the adjacent switching node, bothon the LONG and on the SHORT path of the ring a span bridge request, oracknowledging (head end) , both on LONG/SHORT path, a span bridge request destined toitself.Only switchingnodes performs span Bridge&Switch (see yellow nodes in the example).K byte Pass-through Macro-state entered by each node of the ring (not switching),by-passing bridge request sent on the LONG path by switching node. The same protocolspecified in classic application is used.K byte Pass-through nodes do not perform anyreconfigurationof localK-byte Pass-through nodes are also calledA.Bellato CTO T&A Team- ONDconnectivity.69intermediate nodes. (see grey nodes in the example)

A. Bellato CTO T&A Team - OND 70

Squelching in ring schemes

4F topology

N.T. recovered

E.T. squelched

NE 1SpanBr&Sw

NE 4

NE 2

E.T. squelched onadjacent span

NE 3

N.T. recovered E.T. squelched

(by NE 4)

A. Bellato CTO T&A Team - OND 71

Squelching in ring schemes

Ring squelchingThis type of squelching is needed in 2F/4F classical SPRing, when a node of thering becomes isolated either for node failure or for multiple failures requiring ringswitch at both sides.In this case, due to the ring switch action performed by nodes adjacent theisolated one (i.e. switching nodes), possible traffics terminated into isolated nodeand allocated on same High Priority channels for both sides (West/East), would bemisconnected by accessing the same Low Priority channels. This condition is avoided by inserting at the switching nodes AIS signal onprotection channels, making them unavailable through the ring (the AIS insertionis performed bi- directionally).

A. Bellato CTO T&A Team - OND 75

A. Bellato CTO T&A Team - OND 76

Transport Network Concept

Need for traffic protection

Methods for traffic protection: Protection & Restoration

>

Basics for traffic protection

>

Protection Schemes in Transport Networks

>

Restoration

APPENDIX: Protection schemes in SDH/ Sonet/ OTN

A. Bellato CTO T&A Team - OND 77

Centralized RestorationCentralized restoration ishistorically an application ofnetwork management in TransportNetwork (i.e. SDH), where theamount of operators was verylimited and a completegeographical network (e.g. country)used to be configured andcontrolled by a single(few)manager(s).Centralized Restoration is anapplication provided to an operatorby a single vendor.Centralized Restoration is anetwork application notstandardized, i.e. proprietaryapplications are provided by eachvendor.A. Bellato CTO T&A Team - OND 78

Operating System

DCN NetworkECC

NetworkElement

Transport NetworkGeneric Path

System Evolution - Distributed Restoration

Distributed Restoration ishistorically an application coming fromData Network survivability , wherethe amount of Private Networks (i.e.Data) is unlimited and it becomesunfeasible to configure and controldifferent networks connected to eachother through a single (few)manager(s).Distributed Restoration is anapplication thought for a multivendor enviroment.The de-regulation in Public Networks,has made distributed management,then distributed restoration attractivealso for Transport Network. This impliesa standard activity in order to alignapplications from different vendors.A. Bellato CTO T&A Team - OND 79